The invention relates to apparatus for determining parameters representative of the coagulation and/or the lysis of a coagulable liquid. It relates more particularly to an apparatus commonly named thromboelastography apparatus, for determining such parameters of the blood or derivatives of blood.
A technique for providing measurement of such parameters utilizes a body immersed in the liquid and suspended to a support via vertical torsion means which tends to return said body to a predetermined angular position about the axis of the torsion means. The liquid is received in a receptacle and an oscillatory movement of predetermined frequency and amplitude about the axis of the torsion means is imparted to the receptacle. The amount of oscillatory movement of the body immersed in the liquid is a measure of the viscosity of the liquid. The change of the amount of oscillatory movement with respect to time provides an information about the changes of the properties of the liquid with time, for instance due to coagulation and/or lysis.
A prior art thromboelastography apparatus utilizes a mirror fixed to a torsion wire for providing an indication on the amount of oscillatory movement of the body. A fixed light source directs a light beam onto the mirror and the beam reflected by the mirror is observed directly on a ground glass screen or photographed on a light-sensitive paper carried by a support which moves transversely to the direction of movement of the beam.
FIG. 1 shows the general shape of the curve envelope of the oscillations recorded on a photographic paper in the case of coagulation and subsequent lysis of a blood sample. The curve of FIG. 1 represents the amplitude x of the oscillatory movement of the beam on the paper plotted against time t. Curve 1 is currently called a "thromboelastogram".
The first part 2 of curve 1 corresponds to the initial phase of the coagulation process, before the appearance of fibrin. This initial phase is revealed on the graph by negligible amplitudes and corresponds to a straight portion, commonly called r. When fibrin appears in the blood sample, the amplitude of the oscillations increases with time to a maximum value after which lysis phenomena occur and the amplitude of the oscillations decreases.
The useful parameters for the analysis of coagulation include, besides the time duration represented by segment r: the maximum amplitude A.sub.m of the oscillations and the time period represented by segment k. The beginning of segment k corresponds to the end of segment r, i.e. to an amplitude of oscillation which does not exceed a predetermined value (for instance 1 mm) on the recording paper under predetermined conditions; its end corresponds to an oscillation amplitude which is for instance 20 mm on the recording paper under the same conditions as above.
When the thromboelastogram is obtained by photographic recording, the different parameters of the coagulation, particularly parameters r, k and A.sub.m are measured manually on the photographic picture. In most cases, development of the photographic picture requires time and appropriate facility. Manual measurements are not accurate. Due to the lack of accuracy, a limited number of parameters representative of the variations of the coagulation and/or the lysis can be measured.
It is an object of the invention to remove the above-mentioned disadvantages and to provide a device which allows accurate measuring of parameters representative of the coagulation and/or of the lysis of a coagulable liquid, typically blood.
It is another object of the invention to provide a direct display of parameters representative of the coagulation and/or lysis.
It is a further object of the invention to provide such a device which is rugged, simple and of low cost.
According to an aspect of the invention, there is provided apparatus for determining the viscous behaviour of a liquid during coagulation and lysis thereof or the like. The apparatus comprises vertical torsion means having an end connected to stationary support means and an oscillatory body suspended to the other end of the vertical torsion means (typically a resilient tape) whereby said torsion means tend to return said body to a predetermined angular position about the axis of the torsion means. The apparatus comprises means for supporting a receptacle for the liquid and for imparting to the receptacle and oscillatory movement of predetermined frequency and amplitude about an axis which is substantially coaxial with the axis of the torsion means. The amount of oscillation of the body, which in operation is immersed in the liquid, is measured by an electric system which makes use of electromagnetic detection. For that purpose, the measuring means comprises electrical induction means having a movable element operatively connected to said body for oscillatory movement therewith and a stationary element having output terminal means of a type which delivers, on said terminal means, an electrical signal whose amplitude is representative of the amplitude of the oscillatory movements of said body, and means for measuring the amplitude of said electrical signal.
The variations of the electric output signal may be displayed, for example by means of a graphic recorder. This signal can also be fed to a computer for determining the above-mentioned parameters, particularly r, k and A.sub.m.
In an embodiment of the invention, the inductive movable element is an elongated magnetizable element, e.g. a ferrite bar; this magnetizable element is fast with the torsion means so as to be movable in a plane perpendicular to the axis of the torsion means; in this case, the stationary element may comprise two fixed coils disposed on each side of the movable element so that movement thereof generates a differential induction signal.
The apparatus advantageously comprises demodulator means for generating a signal representing the envelope of the output signal of the induction type sensing means. In this case, the apparatus preferably comprises a comparator for comparing the output signal of the demodulator means with a reference signal representing an oscillation of predetermined amplitude of the torsion means, a clock and counting means for counting the pulses supplied by the generating means. The content of the counting means is stored when the output signal of the demodulator exceeds the reference signal.